In electrophotographic applications, a charge retentive surface (e.g. photoconductor, photoreceptor, or imaging surface) is electrostatically charged, and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways, such as by a modulated laser beam.
Although a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin, adhesives and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom.
A commercially successful mode of cleaning employed hereinbefore in electrophotographic printing machines utilizes a brush with conductive fiber bristles which have suitable triboelectric characteristics to remove residual toner particles from the charge retentive surface. A voltage is applied to the fibers to enhance removal of toner from the charge retentive surface.
However, not all toner and debris is removed from the surface by the brush cleaner. It has been found that toner particles agglomerate with themselves, and with certain types of debris to form a spot-wise deposition that can eventually strongly adhere to the charge retentive surface. These spots range from 50 .mu.m to 500 .mu.m in diameter, but typically are about 200 .mu.m in diameter. The agglomerate debris particles range in material compositions from strictly toner to a broad assortment of toner, adhesives, and plastics and debris from paper. The spots cause a copy quality defect showing up as a black spot on a background area of the copy which is the same size as the spot on the photoreceptor. The spot on the copy varies slightly with the exact machine operating conditions, but cannot be deleted by control of the the machine process characteristics. The presence of agglomerate spots tends to be particularly predominant with the use of recycled-content paper in the printing machine, as more paper debris is often present on recycled-content paper than on non-recycled content paper. Also, the need for effective agglomerate spot removal may be more critical with the use of recycled-content paper because pre-existing spots often appear on the surface of this type of paper which remain after the image has been transferred. In studying the formation of these spots, it was noted that most of the spots appeared instantaneously on the charge retentive surface, i.e., most spots were not the result of a continuing nucleation process. It was subsequently noted that newly deposited spots were more weakly adhered to the surface than older spots.
Agglomerate spot cleaning blades ("spots blades") have been used for removal of agglomerate particles from a charge retentive surface, wherein a relatively lower load is applied to the blade so that the various problems associated with the frictional sealing contact that must occur in the normal cleaning engagement of blades with a charge retentive surface are avoided. Prior art systems wherein a spots blade is used in conjunction with a primary cleaner have utilized an air stream/vacuum removal system for removal of the agglomerate particles accumulated by the spots blade. In some cases, if an air stream/vacuum removal system has not been incorporated in the design of the machine for such removal, a periodic maintenance step is required for manual removal of the accumulated particles from the spots blade.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 4,989,047 issued to Jugle et al. discloses an apparatus for cleaning an electrophotographic printer imaging surface. The cleaning apparatus includes a primary cleaner device in combination with a secondary cleaning device. The secondary cleaning device consists of a blade holder pivotally connected to the housing. The blade holder holds a cleaning blade in frictional contact with the imaging surface, arranged at a low angle of attack and to which a relatively low load is applied for the removal of toner and other debris agglomerates. An air flow path is described to assure that the air stream caused by movement of the brush and a vacuum collection arrangement removes collected agglomerate particles from the spots blade.
U.S. Pat. No. 5,031,000 issued to Pozniakas discloses a floating support assembly which enables the secondary cleaning blade to float relative to the charge retentive surface. This floating support assembly is loaded with a weight selected to maintain the blade in contact with the charge retentive surface, and has a stop to limit the range of movement of the floating blade. An air stream is disclosed for removal of accumulated agglomerate particles from the spots blade, and alternatively, manual removal of the agglomerate particles by periodic maintenance is disclosed.
U.S. Pat. No. 4,819,031 issued to Thayer et al. discloses a multi-vaned toner removal member for transport of toner removed from the photoreceptor belt surface by a primary cleaning blade. The vanes, or blades, mechanically remove toner accumulated by the cleaning blade and transport toner to an auger arrangement.